NMR Resonance Frequency Research Articles

Simultaneous multicompartment intracellular Ca2+ measurements in the perfused heart using 19F NMR spectroscopy

Although Ca2+ transport regulation at subcellular organelles is of great interest, only limited methodology has been available for measuring organellar [Ca2+] levels. The present study employs the 19F NMR resonance frequency of 4F-BAPTA to measure free [Ca2+]. In 4F-BAPTA loaded perfused rabbit hearts, two 19F NMR resonances were clearly observed. The frequency of one was consistent with cytosolic [Ca2+] levels. Responses to agents that after sarcoplasmic reticulum function identified the other resonance as originating from that organelle. The experiments demonstrate the utility of NMR shift indicator methodology in obtaining simultaneous multi-compartment intracellular [Ca2+] measurements and in enabling organellar [Ca2+] measurements to be made from within intact living tissue.

NMR Frequency Shift under Sample Spinning

Abstract It is shown that, by using an RF coil of suitable shape, sample spinning around an axis parallel to the main field produces a shift of the NMR resonance frequency. This effect is experimentally verified on1H and119Sn in liquid samples. A general discussion of sample spinning and frequency shift is given in connection with the rotating-frame picture. Several possible applications are described.

NMR study of the effect of hydrogen on YBa 2Cu 3O 6

Previous studies have shown that when hydrogen is added to the superconductor YBa 2Cu 3O 7 (O 7), it affects many of its properties, as if chain oxygen were removed. Hence the effect of H on the material should be quite different when these oxygen atoms are missing. We have therefore studied the influence of H on YBa 2Cu 3O 6 (O 6). In contrast to the case of O 7, the 89Y NMR resonance frequency is independent of x; instead a second line evolves that is shifted to a higher frequency with respect to the original line. The results confirm that hydrogen in O 6 qualitatively plays a different role than hydrogen in O 7. The quadrupole interaction of 2H in the material yields a coupling constant e 2qQ h of about 250 kHz which indicates that the hydrogen forms an O-H bond. X-ray diffraction results are also discussed.

Determination of the resonance frequency ratio of the 31P and 1H NMR resonance shift standards 85% orthophosphoric acid and tetramethylsilane

AbstractThe NMR resonance frequency ratio of the 31P NMR resonance shift standard 85% orthophosphoric acid (H3PO4) and the 1H standard tetramethylsilane (TMS) was determined by means of the ‘dispersed phase’ method. The Ξ value, equal to 108 times the resonance frequency ratio, was 40480737.0 ± 0.2 Hz at 25°C. A small dependence on temperature (−0.11 Hz °C−1) and on phosphoric acid concentration (−0.50 Hz %−1) was observed around 25°C. Traces of iron in phosphoric acid were found to have a negligible effect on Ξ values, although line widths increased. The determination of Ξ allows accurate referencing of 31P NMR spectra relative to the 1H resonance of internal TMS or of a secondary 1H shift standard. The accuracy of the 31P NMR resonance shift scale is primarily limited by the uncertainty of solvent‐induced 1H resonance shifts of TMS.

Optical NMR and ESR Dipole-dipole and Fermi contact interactions

The quantum theory of nuclear magnetic dipole/laser induced electronic magnetic dipole interactions in optical NMR is developed for atoms in terms of the interaction between the total electronic and nuclear spin angular momenta. It is shown that a circularly polarised laser co-axial with the static magnetic flux density of a conventional NMR spectrometer (of any type) induces an electronic magnetic dipole moment in an atom or molecule, a moment which sets up a magnetic field at the nucleus, thus changing the effective magnetic field and NMR resonance frequency. This mechanism appears to be comparable in magnitude to Landé coupling between the anisotropic, or vectorial, polarisability of the atom and the nuclear spin angular momentum. Dipole-dipole and Fermi contact interaction between the vectorial polarisability and the nuclear spin angular momentum is explored through the appropriate terms in the ONMR interaction energy. Fermi contact interaction is nonzero, generally in a liquid sample.

7Li and 11B nuclear spin lattice relaxation in B 2O 3 + 0.7Li 2O + XLiCl glassy fast ionic conductors

Nuclear spin-lattice relaxation rates, R 1 , are reported for lithium chloro-borate glassy fast ionic conductors for both the mobile 7 Li nuclei and the stationary 11 B nuclei, as functions of temperature and NMR resonance frequency. The 7 Li relaxation is driven by the lithium diffusion via quadrupole interactions. The data for all frequencies can be fitted by assuming a single correlation function of the form exp(−( t / τ c *) β ). In the fit a thermally activated correlation time, τ c *, is assumed with an effective activation energy E a * = 7400 K, higher than the one deduced from dc conductivity measurements. It is argued that the correlation function (CF) which determines the conductivity and the CF which determines the NMR relaxation may differ in the presence of collective effects in the lithium diffusion. The 11 B data indicate that the nuclear relaxation proceeds via a Raman two phonon process involving internal vibrational modes of the BO 4 units heavily damped by reorientational motion. The data are fitted by an expression for R 1 derived from an extension of the Van Kranendonk two phonon relaxation mechanism in insulators. The activation energy for the damping frequency is compared with E a = β E a * which should represent the ‘single particle’ energy barrier for the lithium motion.

51V and 93Nb high resolution NMR study of NbVO5

NbVO5 is characterized by 51V and 93Nb NMR resonance frequencies strongly upfield shifted when compared to those in model compounds V2O5 and LiNbO3. The chemical shift anisotropy dominates the 51V observed spectrum in a magnetic field of 11.7 T. The asymmetry parameter ηc is 0.2 and the quadrupole coupling constant is relatively small (1 MHz). The quadrupolar Hamiltonian overwhelmingly dominates the 93Nb spectrum (ηQ = 0.9) and the quadrupole coupling constant is huge (16.5 MHz). In agreement with the structure obtained from the x-ray powder diagram the isotropic chemical shift of 51V suggests that NbVO5 is indeed an orthovanadate. Interestingly, in NbVO5 the isotropic chemical shift of 93Nb reveals a better shielding of the 93Nb nucleus and a lower electric field gradient than in LiNbO3. Nb octahedra in NbVO5 are sharing corners whereas they share edges in LiNbO3.

Nuclear magnetic resonance microscopy

Nuclear magnetic resonance imaging can reach microscopic resolution, as was noted many years ago, but the first serious attempt to explore the limits of the possibilities was made by Hedges. Resolution is ultimately limited under most circumstances by the signal-to-noise ratio, which is greater for small radio receiver coils, high magnetic fields and long observation times. The strongest signals in biological applications are obtained from water protons; for the usual magnetic fields used in NMR experiments (2-14 tesla), receiver coils of one to several millimeters in diameter, and observation times of a number of minutes, the volume resolution will be limited to a few hundred or thousand cubic micrometers. The proportions of voxels may be freely chosen within wide limits by varying the details of the imaging procedure. For isotropic resolution, therefore, objects of the order of (10μm) may be distinguished.Because the spatial coordinates are encoded by magnetic field gradients, the NMR resonance frequency differences, which determine the potential spatial resolution, may be made very large. As noted above, however, the corresponding volumes may become too small to give useful signal-to-noise ratios. In the presence of magnetic field gradients there will also be a loss of signal strength and resolution because molecular diffusion causes the coherence of the NMR signal to decay more rapidly than it otherwise would. This phenomenon is especially important in microscopic imaging.

Micellar behavior of a nonionic surfactant, surfynol 465, from carbon-13 NMR resonance frequencies in water-d2

Micellar behavior of a nonionic surfactant, surfynol 465, from carbon-13 NMR resonance frequencies in water-d2

Static quadrupolar perturbed NMR in structurally incommensurate systems. I. Electric-field-gradient tensor.

An approach for describing and characterizing quadrupolar perturbed NMR spectra in incommensurate phases in terms of structural parameters is proposed. The method is based on the superspace formalism, which is widely used in the structural analysis of phases of this type. It is shown that the modulation functions defined along the ``internal'' space, which so far have been used for describing the atomic displacements with respect to the nondistorted basic structure, can also be applied to other microscopic quantities, such as the electric-field-gradient tensor (EFG) and the NMR resonance frequencies. The use of these modulation functions is proved to be an appropriate method for describing the NMR frequency distributions in incommensurate phases. The conditions imposed on the EFG distributions and their resultant NMR spectra by the superspace symmetry of the incommensurate structure can be readily obtained. It is proved for a general case that the degeneracies and symmetries for the rotation patterns of the continuous NMR spectra in these phases correspond to those which the average structure would exhibit for its discrete lines. The relation between the modulation functions of the EFG and those of the atomic displacements is discussed in a general context, and also on the basis of Landau theory. The so-called ``local'' and ``nonlocal'' models are then compared to the present analysis. It is shown that while the first one is too restrictive, the second one implies in general a local approximation. In the subsequent work these general results are applied to the $^{87}\mathrm{Rb}$ NMR satellite transitions in ${\mathrm{Rb}}_{2}$${\mathrm{ZnBr}}_{4}$.

Parity non-conservation and NMR observables. calculation of Tl resonance frequency differences in enantiomers

The formulas giving the parity non-conservation contribution to the nuclear magnetic shielding σ, the indirect spin-spin coupling J, the spin rotation coupling M are derived using Ramsey's formalism. From a relativistic Hückel molecular calculation, NMR resonance frequency differences close to 1 mHz ( v( 205 Tl) = 288.5 MHz ) are obtained for three couples of mirror-image molecules.

NMR lineshape and phase soliton effects in incommensurate Rb2ZnCl4

In incommensurate systems the NMR, NQR or EPR resonance frequency varies in space in a way which reflects the spatial variation of the incommensurate modulation wave. An evaluation of the magnetic resonance lineshape for the case of a multi-soliton lattice is presented for different ratios between the soliton width and the inter-soliton spacing as well as for different relations between the resonance frequency and the incommensurate order parameter. The results are compared with the experimental data in Rb2ZnCl4. It is found that in this system the soliton width is large compared with the inter-soliton spacing over most of the incommensurate phase. The temperature variation of the phase soliton density has been determined. The non-classical value of the critical exponent beta =0.35+or-0.03 for the amplitude of the order parameter demonstrates that the whole incommensurate phase is critical in this one-dimensionally modulated system.

NMR multiple echoes observed in solidHe3

A large number of echoes-called multiple echoes-following two isolated NMR radio-frequency pulses separated by a time $\ensuremath{\tau}$, have been observed in bcc $^{3}\mathrm{He}$. A quantitative theory of this phenomenon is given, taking into account the nonlinear effect of the nuclear demagnetizing field in the equation of motion of the magnetization. In a magnetic-field gradient $G$, just before the second pulse at time $\ensuremath{\tau}$, the nuclear-spin transverse magnetization has a helical configuration of pitch $\ensuremath{\gamma}G\ensuremath{\tau}={k}_{0}$, which is converted by the second radio-frequency pulse into a sinusoidal modulation of the magnetization along the magnetic field gradient. The corresponding sinusoidal demagnetizing field modulates spatially the NMR resonance frequency so that the transverse magnetization is a superposition of helical configurations with pitch $p{k}_{0}$ (multiple of ${k}_{0}$), yielding multiple echoes at times $p\ensuremath{\tau}$. A detailed comparison with the experimental results obtained at high temperatures ($300 \mathrm{mK}<T<1 \mathrm{K}$) and low temperatures ($1<T<20$ mK), leads to a satisfactory agreement with the experiments. The main practical application of the multiple-echo study is to provide a method of measurement of the absolute value of the nuclear-spin susceptibility without knowing the shape or the number of spins of the sample. The transverse relaxation time ${T}_{2}$ and the diffusion coefficient $D$ are also obtained with this analysis. When applied to the low-temperature measurements, the multiple-echo analysis has pointed out, for the first time, the increase of the magnetic susceptibility of solid $^{3}\mathrm{He}$ in the paramagnetic phase near the ordering temperature ${T}_{c}$, while in contrast the relaxation times ${T}_{1}$ and ${T}_{2}$ and the diffusion coefficient $D$ do not change appreciably, even just above ${T}_{c}$.

Determination of kinetic parameters by the frequency dependence of the NMR coalescence temperature

A method is described in which one determines the rate parameters for chemical exchange between two equally populated uncoupled sites by measuring the dependence upon NMR resonance frequency of the temperature at which the corresponding two high-resolution lines coalesce. The method is relatively simple and, when applicable, gives good accuracy with modest effort. It was tested by observing the coalescence of the methyl group resonances due to internal rotation in neat dimethyl-formamide, -acetamide, and -propionamide, at 60, 100, and 220 MHz. The results include an entropy of activation ΔS‡=0±0.2 e.u. for the three compounds, and an enthalpy, ΔH‡ of 20.9, 18.0, and 17.1±0.1 kcal/mole, respectively, where the errors indicate the approximate accuracy of the results.

Memory effects in the NMR frequency shifts

The narrowing of the heat-bath correlation function by decreasing the sample temperature in a molecular system with a cooperative motion, causes the shifting of the NMR resonance frequency, as predicted by the memory-function approach.

The thermal conductivities of certain liquids

The electronic g factor carries highly useful information about the electronic structure of a paramagnetic species, such as spin-orbit coupling and dia- or paramagnetic (de-)shielding due to local fields of surrounding electron pairs. However, in many cases, a near “spin-only” case is observed, in particular for light elements, necessitating accurate and precise measurement of the g factors. Such measurement is typically impeded by a “chicken and egg situation”: internal or external reference standards are used for relative comparison of electron paramagnetic resonance (EPR) Larmor frequencies. However, the g factor of the standard itself usually is subject to a significant uncertainty which directly limits the precision and/or accuracy of the sought after sample g factor. Here, we apply an EPR reference-free approach for determining the g factor of atomic nitrogen trapped within the endohedral fullerene C60:[email protected]60 in its polycrystalline state by measuring the 1H NMR resonance frequency of dispersing toluene at room temperature. We found a value of g=2.00204(4) with a finally reached relative precision of ∼20 ppm. This accurate measurement allows us to directly compare the electronic properties of [email protected]60 to those found in atomic nitrogen in the gas phase or trapped in other solid matrices at liquid helium temperature. We conclude that spin-orbit coupling in [email protected]60 at room temperature is very similar in magnitude and of same sign as found in other inert solid matrices and that interactions between the quartet spin system and the C60 molecular orbitals are thus negligible.